1. Field of the Invention
The invention relates to an improved tip for oculistic surgery, particularly for the removal of cataract by the cataract “phacoemulsification” technique.
2. Description of the Prior Art
More particularly, the invention concerns a tip of the above kind to be used in the ultrasound phacoemulsification technique with a 1 mm incision.
As it is well known, the “phacoemulsifier” substantially is an instrument comprised of a control unit and a “handle”, by which the surgeon makes the intervention.
At the end of the handle, a “needle” or “tip” is coupled, oscillated at a ultrasonic frequency by a “piezoelectric” or “magneto-restrictive” system, housed within the same “handle”.
“Handle” is further provided with an infusion and suction system, the first one of which generally acts by gravity, while the second latter is assisted by a vacuum pump.
Suction system is realised in such a way to act coaxially through the needle and is useful to suck the crystalline (cataract), crushed by the vibratory motion of the same needle.
Instead, the infusion system acts concentrically and outside the needle, irrigating within the eye a physiological solution to restore the liquid sucked along with the crystalline.
Particularly, the irrigation passes through the annular space created by a small “sleeve”, generally comprised of silicone, coaxially placed outside the needle.
In the “traditional” technique, the needle—sleeve assembly is introduced within the “front chamber” of the eye, by a corneal incision having dimensions proportional to the diameter of the needle (2.5–3 mm).
Present trend in cataract “phacoemulsification” is that of reducing at most the extension of the corneal incision, in order to minimise the surgical trauma (post surgical astigmatism, etc.).
This was possible thanks to the evolution of foldable lenses replacing the crystalline, requiring corneal incisions always smaller to be implanted.
One of the most recent surgical techniques following this tendency is that providing the irrigation separated from the needle and carried out by a suitable cannula introduced within the eye through a second corneal incision.
This technique allows employing very small phacoemulsification tips, without irrigation sleeve, requiring very much reduced corneal incisions (1 mm).
It is well evident that two opposed incisions of 1 mm, are less traumatic for the corneal tissue than one incision of 3 mm; furthermore, said “bimanual” technique give to the surgeon a best action capability.
One of the complications that could occur employing said surgical technique is the more or less marked burning of the cornea in correspondence of the two incision flaps though which the needle passes, due to the heat generated by friction caused by the friction of the needle against the cornea.
To aggravate the problem contributes the movements of the needle, made by the surgeon transversely with respect to the corneal incision.
Up today, very few are the solutions trying to solve said complication acting on the needle dynamic friction coefficient, said needle being comprised of 5 grade titanium alloy, due to mechanical needing.
In this situation, it is well evident how it could be advantageous a valid solution that would give remarkable advantages in case of “via pars-plana” phacoemulsification, a kind of intervention by which the crystalline is reached from the rear part of the ocular bulb through the sclera, since for said intervention longer and thinner needles are employed, without irrigation sleeve.
A first solution, already suggested, is that of carrying out a better surface finishing (polishing) of the part of the needle that could contact the corneal incision.
Limits of said solution are due to the fact that, even obtaining a certain reduction of the friction coefficient, it is bound to the kind of material (5 grade titanium alloy) used to manufacture the needle.
A subsequent solution already suggested in the art, and subject of the Italian Patent Application No. RM97U000159, filed on Jul. 30, 1997 in the name of Optikon 2000 S.p.A., provides a partial coating of the needle by PTFE.
The last solution, even if remarkably reduces the dynamic friction coefficient between needle and cornea, has remarkable drawbacks.
PTFE deposition method, particularly in the titanium alloy by which the needle is realised, does not guarantee a good adhesion; thus, the coating easily separates, particularly close to the transition zone between coating and anti-reflex treatment.
Always due to the PTFE deposition method, thickness of the coating is not uniform and in any case is often rather high with respect to the needle dimensions, thus causing an increase of the outer diameter of the same of about 400 μm, that is disadvantageous for its use.
Finally, PTFE coating, which is particularly soft, is not so much resistant to mechanical stresses (abrasion, scratch, etc.) to which it can be subjected during its use.